Subject: [PWE3] additional text for the TDM control protocol extensions draft

From: "Yaakov Stein" <[email-masked]>
Date: Wed, 12 Mar 2008 17:14:15 +0200

Hi all
 
The TDM control protocol extensions draft
draft-ietf-pwe3-tdm-control-protocol-extensi-06.txt 
was sent to the IESG for processing. It requires several IANA actions,
and we have been informed
that one of which will require some additional text to be added to the
draft.

The problem is with the TDMoIP AAL2 Options interface parameter. The
base length of this field is 8 bytes, 
but there is an optional extension that is usually just a byte or two in
length,
but in unusual cases could theoretically be very lengthy.

Because of assumptions concerning the amount of state memory that needs
to be set aside for 
LDP implementations, there is concern about allowing allocations of TLVs
which could potentially be lengthy. 
We have agreed to add an informative note clarifying that in cases where
this parameter IS indeed lengthy,
there would be a limitation on the number of such PWs a PE needs to
support.

In particular, we intend adding the following text to section 3.5 of the
draft before its continued processing by the IESG :

   The length of basic TDMoIP AAL2 Options interface parameter is 8
bytes, 
   and when the optional CID mapping bases field is used there is one
additional byte for each trunk transported. 
   Thus if 4 trunks are being supported, this message occupies 12 bytes.

   Since there can be no more than 248 CIDs in a given PW, this can
never exceed 256 (when precisely one timeslot is used per trunk), 
   but for fully populated E1s it is less than 17 bytes, and for full
T1s it can not exceed 19 bytes. 

   A single PE is not required to support more than 10 AAL2 PWs 
   (i.e., up to 2480 individual channels, which is more than carried by
a fully populated STM1). 
   Thus the typical memory required to store the AAL2 mapping
information is not more than 200 bytes per PE, 
   although for worst case scenarios may reach 2560 bytes. 

Y(J)S

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